Buildings in a need of renovation represent a large energy consumption source. However, it is no longer enough to focus just on the energy framework of buildings without particular interest in the indoor environment. Windows are one of the building elements on the façade that, if adequately sized, can provide with appropriate visual comfort, heat gains and natural ventilation. Nevertheless, natural ventilated buildings cannot always provide with the required temperature and ventilation rate and in addition its control is always user dependent. For this reason, this paper focuses on the performance and indoor environment provided by two different designs of ventilated windows. This technology allows a self-controlled ventilation where the air supplied to the room is at a higher temperature than the air outdoors. In addition, its dynamic working modes can adapt to the different indoor and outdoor conditions. Influence of the window performance in indoor environment in a primary school is analyzed. Results show that the window performance is enhanced the most together with a mechanical extraction. With regards to the thermal performance, the height of the cavity and the inclusion of blinds between the panes improve the ability of preheating the air. However, this phenomena is negatively affected by high flow rates. In terms of indoor comfort, a first window design does not provide with enough ventilation and suitable control strategy to remove the excessive CO2 concentrations reported in the rooms. Consequently, a new window design together with a suggested control strategy aims to address the problem of poor air quality at the school. Further studies will permit to test the suggested control strategy and prove that ventilated windows are a solution that can serve high and variable occupancy loads and avoid a decentralized ventilation system. There is a large potential in which ventilated windows would be an effective solution. However, it is crucial for their effectiveness to have a controlled mechanical exhaust, a window design that enhances the temperature rise through the window and assure a system with enough number of windows in order provide an optimal air flow rate.